> LLMs have an impressive amount of ability to do knowledge-transfer between domains, it only makes sense that that would also apply to programming languages, since the basic underlying concepts (functions, data structures, etc.) exist nearly everywhere.

That would make sense if LLMs understood the domains and the concepts. They don't. They need a lot of training data to "map" the "knowledge transfer".

Personal anecdote: Claude stopped writing Java-like Elixir only some time around summer this year (Elixir is 13 years old), and is still incapable of writing "modern HEEX" which changed some of the templaring syntax in Phoenix almost two years ago.